Pump and method of driving same

ABSTRACT

A fluid transfer device such as a reciprocating pump, preferably of the diaphragm type suitable for use with an airless spray-gun for painting and the like, having a pumping side for the fluid to be pumped and a driving side driven through a piston through a solution or mixture of liquid and gas, such as oil and air. Under throttled or standby operation conditions, reduced diaphragm movement is accommodated without changing the piston stroke by reducing the volume of the driving liquid and by releasing gas from the reduced volume of liquid to prevent vaporization and condensation of the driving fluid itself. A dead space is provided on the pumping side allowing some diaphragm movement into the pumping side even when completely closed so that only a small proportion of driving liquid is released and only a small amount of gas is freed from the driving liquid to accommodate the reduced diaphragm movement during the full piston stroke. The loading and unloading of the driving fluid on the power and suction strokes of the piston is controlled so that the driving fluid is always above its vapor pressure. The gas is released from the driving liquid according to Henry&#39;&#39;s Law.

United States Patent Wagner 51 Aug. 1, 1972 [54] PUMP AND METHOD OF DRIVING SAME A [72] Inventor: Josef Wagner, Markdorferstr. 165,

Friedrichshafen-Spaltenstein, Germany 22 Filed: Dec.2l, 1970 21 Appl.No.: 99,823

[56] References Cited UNITED STATES PATENTS 12/1951 Scherger et al. ..4l7/388 1/1963 Eifel ..417/388 Primary ExaminerRobert M. Walker Attorney-Hill, Sherman, Meroni, Gross and Simpson 5 7 ABSTRACT A fluid transfer device such as a reciprocating pump, preferably of the diaphragm type suitable for use with an airless spray-gun for painting and the like, having a pumping side for the fluid to be pumped and a driving side driven through a piston through a solution or mixture of liquid and gas, such as oil and air. Under throttled or standby operation conditions, reduced diaphragm movement is accommodated without changing the piston stroke by reducing the volume of the driving liquid and by releasing gas from the reduced volume of liquid to prevent vaporization and condensation of the driving fluid itself. A dead space is provided on the pumping side allowing some diaphragm movement into the pumping side even when completely closed so that only a small proportion of driving liquid is released and only a small amount of gas is freed from the driving liquid to accommodate the reduced diaphragm movement during the full piston stroke. The loading and unloading of the driving fluid on the power and suction strokes of the piston is controlled so that the driving fluid is always above its vapor pressure. The gas is released from the driving liquid according to Henrys Law.

27 Claims, 9 Drawing Figures PATENTED B I 1973 SHEET 2 0F 4 INVENTUR F ,1 EYS PATENTEDAHB' 1 I912 3.680.981

SHEET 3 OF 4 I NVEN TOR.

J0 5 5F Woe/v63 BY AITTORNEYS PATENTEDAUQ 1 1912 3,680,981

sum u or 4 INVENTOR.

Jo 5 5F W4 a/vk BY ATTORNEYS PUMP AND METHOD OF DRIVING SAME BACKGROUND OF THE INVENTION densation causes rapid erosion and corrosion of the pump parts and useful driving fluids are limited to low I boiling liquids.

SUMMARY OF THE INVENTION The deficiencies of the prior art liquid driven diaphragm pumps are completely eliminated and improved pumping efficiency and useful pump life are provided by this invention which eliminates vaporization and condensation of driving liquid in a liquid driven diaphragm pump. According to this invention, the pump diaphragm is variably driven from a reciprocating piston having a constant stroke through a variable volume of liquid having a gas dissolved therein under conditions which never allow the liquid to vaporize and which operate according to l-Ienrys Law. While it is preferred that the driving liquid have the gas dissolved therein under one phase of operation, it is possible to use a driving liquid composed of a mixture of liquid and undissolved gas which expand under certain operating conditions.

An important feature of this invention is the complete elimination of vaporization of driving liquid in the operation of a liquid driven diaphragm pump and the maintenance of the liquid phase of the driving liquid at all times.

Another important feature of this invention is the provision of a dead space occupied only by air, paint solvent vapor or the like compressible material, on the pumping side of the diaphragm which allows the diaphragm to move to prevent vaporization of driving liquid even under conditions where the flow of liquid being pumped is throttled or completely stopped. In spray-gun usage of the pumps of this invention, interruption of the flow of paint or the like being pumped is sudden and may be quite frequent. Displacement of the diaphragm at least partially into the pumping chamber during these sudden stop periods provides for an enlarged volume in the driving liquid chamber with a reduced overflow of driving liquid on the first power stroke following throttling or shut-off so that the next suction stroke cannot result in vaporization of any dn'ving liquid because sufficient gas will be released from the liquid to fill the chamber without reducing pressure sufiicient to accommodate boiling of the liquid.

More particularly, according to this invention, the driving liquid is preferably a lubricant such as oil and the gas is preferably air dissolved in this oil. Under atmospheric temperature and pressure conditions, about 4-8'% by volume of air is dissolved in a lubricating oil of relatively low viscosity and relatively high boiling point. A light hydraulic oil is satisfactory. Gases other than air might be dissolved in a suitable driving liquid, such as for example, nitrogen, oxygen, hydrogen, carbon dioxide and the like. Where lubrication is not a problem, the driving liquid may be water.

In general, the gas containing driving liquid is maintained under temperature and pressure conditions which will allow release of the dissolved or entrained gas only on the suction stroke of the pump following the throttling or stoppage of the pumping operation. The released gas is reintroduced into the driving liquid upon resumption of the pumping operation.

To ensure against possible vaporization of the driving liquid, the pressure of the driving liquid is never released to a point even close to the vapor pressure of the liquid and the pressure is maintained from 10 to times the pressure at which vaporization could occur.

Temperatures of the driving fluid are maintained sufficiently low to avoid vaporization even at the lowest operating pressures by reducing any required recirculating of the driving fluid to a minimum.

After throttling or complete stoppage of flow of the liquid being pumped, the remaining volume in the driving liquid chamber is harmonized with the piston stroke so that the lowest pressure produced on the suction stroke of the piston remains above the boiling pressure of the driving liquid and the return stroke volume of the chamber is completed with gas freed or expanded from the driving liquid thereby preventing vaporization. At the end of the suction stroke the driving liquid chamber is completely filled with a mixture of the driving liquid and the released gas.

To ensure that this remaining volume of the driving I liquid is sufficiently great to contain enough gasfor completely filling the driving liquid chamber, the aforementioned dead space is provided in the pumping chamber even during full pumping operation so that diaphragm movement into the pumping chamber is not completely stopped even upon full throttled no-flow standby conditions.

The pumping chamber is fed through an inlet check valve and the pumped liquid is withdrawn through an outlet check valve and a control valve such as a spraygun. The chamber on the opposite side of the diaphragm containing the driving liquid and the driving piston is connected to a source chamber through a bypass with a pressure limiting valve and through a refill passage for replenishing the pumping liquid. The pressure limiting valve is adjustable to control the delivery pressure of the pump.

The pump piston must not be retracted during the suction stroke with too great a velocity since the gas dissolved or entrapped in the liquid may not be given enough time to be freed from the liquid. If the suction stroke proceeds at a rate slow enough to release the dissolved or entrapped gas, only enough gas will be freed to maintain a constant stroke without ever releasing the pressure sufficient to permit boiling of the driving liquid. The gas separation thus obeys the law of Henry, and it is only when the pump piston is withdrawn with too great a velocity that a hollow space created ahead of the piston may be filled with vapor of the driving liquid which during the next pressure stroke, of course, leads to the undesirable cavitation. ,The maximum pump velocity is chosen so that the law of Henry may apply to the freeing of the gas. Preferably, the piston should not have a retracting velocity above 1.0 to 1.5 meters per second.

To prevent the dead space in the pumping chamber from becoming filled with the pumping liquid during the subsequent suction strokes after a throttling or stoppage of flow of pumping liquid, a spring loaded inlet valve is preferably provided such that the spring characteristic and the mass inertia of the valve will not permit the valve to be opened by reduced pressure in the dead space of the pumping chamber. A spring having a rate of 75 gramsper millimeter and a closing load of 300 grams is sufficient to maintain the dead space.

It is then an object of this invention to provide an improved diaphragm pump capable of being fully throttled and method of pumping through a driving liquid without vaporizing the driving liquid.

Another object of this invention is to provide a liquid driven diaphragm pump, useful for spray painting, having a wide range of delivery pressures and delivery rates without bypassing the material being pumped and without effecting vaporization of the driving liquid.

A further object of this invention is to provide a method of driving a diaphragm or the like through a liquid containing a dissolved or admixed gas freed during a throttling of the diaphragm stroke to prevent vaporization of the driving liquid.

A still further object of the invention is to provide a liquid driven diaphragm pump operating according to the law of Henry.

Another object of the invention is to provide a diaphragm pump with a dead space on the pumping side of the diaphragm which will accommodate movement of the diaphragm even when flow of the pumping liquid is stopped.

Another object of the invention is to provide a diaphragm type paint spray pump with an inlet valve so correlated with a liquid driven diaphragm as to maintain a void filled only with compressible air, vapors or the like in the pumping chamber during all conditions of operation.

A still further object of the invention is to provide a diaphragm pump driven by a constant stroke reciprocating piston through a lubricating liquid having a gas dissolved therein which is released from the liquid when the pumping operation is throttled or stopped.

Another object of the invention is to provide a diaphragm pump driven by a constant stroke reciprocating piston through a lubricating liquid having a gas dissolved therein and a dead space on the pumping side of the diaphragm so correlated with an inlet valve as to accommodate limited movement of the diaphragm when flowof the pump material is stopped so that only a small amount of the driving liquid need be released to accommodate the limited stroke of the diaphragm.

Other and further objects of this invention will become apparent to those skilled in this art from the following detailed descriptions of the annexed sheets of drawings which, by way of a preferred embodiment, show one form of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat diagrammatic longitudinal sectional view with partsin elevation of a diaphragm pump according to this invention for pumping paint to a spray-gun and illustrating the positions of the parts at the end of a suction stroke; v

FIG. 2 is a view similar to FIG. 1 but illustrating the positions of the parts at the end of a pressure stroke;

FIG. 3 is a view similar to FIGS. 1 and 2 but illustrating the position of the parts during a pressure stroke following full throttling of the pumping operation;

FIG. 4 is a view similar to FIGS. 1 to 3 but illustrating the positions of the parts and the condition of the driving fluid at the end of a suction stroke following a pressure stroke after full throttling, as shown in FIG. 3;

FIG. 5 is a longitudinal cross-sectional view, with parts in elevation and with parts broken away, of one form of diaphragm pump according to this invention;

FIG. 6 is an enlarged longitudinal sectional view of the pumping side of the pump of FIG. 4;

FIG. 7 is an enlarged longitudinal sectional view of the driving side of the pump of FIG. 4;

FIG. .8 is an enlarged side elevational detail view with parts shown in cross section of the diaphragm and support plate of the pump of FIG. 4;

FIG. 9 is a plan view of the support plate taken along the line IX-IX of FIG. 8.

DETAILED DESCRIPTION OF THE DRAWINGS In FIG. 1 there is schematically illustrated a diaphragm pump 1 according to this invention having a casing defining a first or pumping chamber 2 fed from a supply container 3 with liquid to be pumped such as paint or the like. Liquid from the container 3 is supplied to the chamber 2 through an inlet pipe 4 and inlet check valve 5; The pressurized liquid or pumpage is discharged through an outlet check valve 6 to a supply hose 7 to a paint spray-gun 8 having a control valve 9 throttling or completely stopping flow from the pumping chamber 2.

The pump 1 has an axially movable diaphragm 10 forming one wall of the chamber 2 and separating this chamber from a driving liquid chamber 11 to which driving pressure is intermittently applied and relieved by means of a piston pump generally identified at 12 and including a cylindrical chamber 13 slidably mounting a cylindrical piston 14 driven by a wobble plate 15 rotated by a driving motor 16.

The wobble plate 15 rotates in a container 17 for the driving liquid which communicates with the driving liquid chamber 11 behind the diaphragm 10 by means of an overflow passage 18 containing an adjustable pressure limiting valve 19. A refill passage 20 also joins the bottom portion of the container 17 with a refill slot 21 in the cylindrical chamber 13 receiving the piston 14. The slot 21 is uncovered by the piston 14 only at the end of the suction stroke of the piston and is otherwise closed by the piston.

The container 17 is partially filled with the driving liquid L to a liquid level LL, and the top of the chamber 17 may be vented to the atmosphere as at V. A spring S urges the piston 14 against the wobble plate 15. The wobble plate 15 in the container 17 agitates the liquid L insuring aeration with air from vent V.

The wobble plate 15 drives the piston 14 through a relatively short stroke from the rearmost suction stroke illustrated in FIG. .1 to the forward end of the power stroke illustrated in FIG. 2, and this reciprocation of When the motor is driven to rotate the wobble plate 15, the piston 14 will be moved forwardly from its rearmost position shown in FIG. against the bias of the spring 47 and will act through the driving liquid to force the diaphragm off of the seating plate 59. The forward movement of the diaphragm in the pumping chamber 2 will discharge paint from the pumping chamber past the check valve 6 to the spray-gun outlet. Then, on the return stroke the diaphragm 10 will be biased back to the position shown in FIG. 5 enlarging the pumping chamber 2 and drawing paint from the inlet 4 through the inlet valve 5. The load of the spring 38 on this inlet valve 5 is such that the valve will not open on the initial retraction of the diaphragm so that the pumping chamber 2 is never filled with a liquid material and the dead space D will be preserved. The contour 33b of the insert ring 33 and the thin membrane portion 57b overlying this contoured portion cooperate with the spring load on the inlet valve to maintain this small dead space D.

In one commercial embodiment of a diaphragm pump for airless spary painting usage according to this invention, the pump chamber 2 of the pump has a capacity of about 19 0.0., the outlet check valve 6 is spring loaded at about 150 grams with the spring having a rate of 60 grams/mm. and the inlet valve 5 is spring loaded at about 300 grams with a spring rate of 75 grams/mm. The diaphragm 10 is spring biased into the chamber 11 by spring 60 at 23.4 kilograms with a rate of 2.93 kg/m.m. When the relief valve 19 is set to open at 240 kg, this pump will deliver a pressure of about 150 kg/cc to a spray-gun 8 having a delivery orificediameter of 0.31 inches. The relief valve 19 may be varied to open at different pressures with a resultant variation in delivery pressure. The orifice size on the spraygun 8 may be changed to vary the delivery pressure at the same relief valve setting. The piston 14 has a stroke of about 8 mm. and the wobble plate 15 is driven at about 1,480 RPM. When such a pump is fully throttled to stop flow from the pumping chamber 2, the amount of driving fluid released through the valve 19 will not be more than about 6 percent of the volume of driving liquid in the chamber 1 1. Then, when the spraygun 8 is opened for full delivery, the driving liquid will be replenished through the passage 20 at the rate of about 0.45 c.c. on each stroke of the piston 14 until the chamber is again filled with the driving liquid and the gas is re-dissolved in this liquid. The wobble plate drive has a wide speed range and is driven slow enough so that the piston cannot retract at a faster rate than the gas can be released.

It should be understood that the pump form of FIGS. 5 through 9 represents only one embodiment of the pump of this invention, and details of construction may be widely varied from this illustrated form without departing from the principles and scope of this invention.

It should be understood that the herein described diaphragm is a preferred fluid propelling member but it could be replaced with a piston, a bellows or the like fluid propelling device without departing from the principles and scope of this invention.

It should also be understood that while the invention is particularly described as embodied in a pump, the

principles of the invention are generally useful in fluid power transfer machines including motors as well as fluid propelling machines and such usage is included within the scope of this invention.

1 claim as my invention:

1. A driven fluid pump device adapted to be throttled and stopped without throttling or stopping the driving input which comprises, means defining a pumping chamber and a driven fluid chamber, a fluid propelling member separating said chambers, a driving fluid in said driving fluid chamber actuating said member and composed of liquid and gas, driving means for alternately pressure loading and unloading said driving fluid, means for releasing some of said driving fluid when loaded above a predetermined pressure to provide a reduced driving volume for reduced actuation of said propelling member, and means maintaining minimum pressure on the driving fluid above the vapor pressure of said fluid whereby any expansion of the reduced driving volume upon unloading will be accommodated by the remaining liquid and gas releasedtherefrom.

2. The device of claim 1 wherein the driving fluid is a liquid having a gas dissolved therein which is released therefrom according to the law of Henry.

3. The device of claim 2 wherein the liquid is a lubricant and the gas is air.

4. The device of claim 1 wherein the fluid propelling member is a diaphragm.

5. The device of claim 1 wherein the driving means is a piston.

6. The device of claimS wherein the piston has a uniform stroke.

7. The device of claim 5 wherein the piston is driven by an eccentric member.

8. The pump device of claim 1 wherein the fluid propellingmember receives pumpage on one side and said driving fluid on the other side and an inlet valve controls flow of pumpage to maintain a dead space on the pumpage side of said fluid propelling member accommodating movement of the member to lessen reduction of the driving volume of said driving fluid during standby operation when no flow of pumpage occurs.

9. The device of claim 8 wherein the fluid propelling member is a diaphragm having a pumpage chamber on one side and a driving fluid chamber on the other side, an inlet valve controls flow of pumpage into the pumpage chamber, a check valve controls flow out of the pumpage chamber, and said two valves cooperate to prevent the pumpage chamber from being completely filled to maintain a dead space of compressible fluid accommodating movement of the diaphragm into the pumpage chamber during throttling or stopping of the pumping.

10. The'device of claim 1 including a supply chamber for driving fluid and a spring loaded valve controlling release of driving fluid to said supply chamber.

11. The device of claim 10 wherein a passageway selectively connects the supply chamber with the driving fluid chamber ahead of the driving means for replenishing said chamber.

12. A driven pump adapted to be throttled or stopped without throttling or stopping the driving imput comprising a housing defining a pumping chamber and a driving liquid chamber, a fluid propelling member separating said chambers, driving means acting on liquid in the driving liquid chamber to actuate said propelling member for pumping fluid through the pumping chamber, a relief valve controlling maximum pressure in said driving liquid chamber and releasing excess liquid from the chamber to accommodate throttled movement of the diaphragm, and means controlling the driving means to maintain pressure on the remaining liquid in the driving liquid chamber above the vapor pressure of the liquid.

13. The pump of claim 12 having a source of driving liquid containing gas dissolved therein communicating with said relief valve to receive excess driving liquid from the driving liquid chamber, and means connecting said source with the driving liquid chamber to replenish the chamber whenever pressure therein is below the pressure of the source.

14. The pump of .claim 12 wherein the pumping chamber is fed through an inlet valve biased to closed position to maintain a dead space accommodating movement of the fluid propelling member into the pumping chamber even when the chamber is closed.

15. The pump of claim 12 wherein the fluid propelling member is a diaphragm and the driving means is a constant stroke piston.

16. A driven diaphragm pump adapted to be throttled and stopped without throttling or stopping the driving input which comprises a housing having a diaphragm chamber, a diaphragm in said housing spanning said chamber and dividing the chamber into a pumping chamber and an opposed driving liquid chamber, a spring biased inlet valve for admitting pumpage to said pumping chamber, an outlet valve controlling flow of pumpage from said pumping chamber, a source of lubricating liquid having air dissolved therein, means bleeding liquid from said source to said driving chamber, a relief valve controlling flow of liquid from the driving chamber back to the source, a piston acting on liquid in said driving chamber to load and unload said liquid for reciprocating said diaphragm to draw pumpage through the inlet valve into said pumping chamber and to discharge pumpage from the pumping chamber through the outlet valve, means driving said piston through a stroke to act through the liquid for forcing a full stroke of the diaphragm whenever pressure in the pumping chamber is below the pressure of the driving liquid, said relief valve releasing driving liquid from the driving chamber back to the source when pressure in the pumping chamber exceeds pressure on the driving liquid, the spring load on said inlet valve to the pumping chamber being effective to maintain a dead space in the pumping chamber accommodating movement of the diaphragm into the pumping chamber even when the outlet valve is closed thereby minimizing release of driving liquid through the relief valve upon throttled operation of the pump, and means limiting the stroke of the piston to maintain the driving liquid volume less than a volume occupied by the liquid and available air from the liquid to always sustain the liquid above its vapor pressure whereby reduced throttled diaphragm strokes are accommodated by reducing the volume of driving liquid and releasing air from the reduced volume of liquid to prevent vaporization of the liquid.

17. The pump of claim 16 wherein the piston closes the bleeding means except at the end of its suction stroke.

18. The pump of claim 16 wherein the piston is spring biased against a wobble plate providing the driving input.

19. The pump of claim 16 wherein the outlet valve is in a spraygun receiving pumpage from the pumping chamber.

20. A diaphragm pump comprising a housing defining a chamber for a source of lubricating liquid containing dissolved air, a driving chamber for said liquid and a pumping chamber, a diaphragm separating said driving and pumping chambers, a piston separating said source and driving chambers, means reciprocating said piston to load and unload liquid in said driving chamber, a passageway venting the source chamber to the driving chamber only when the piston unloads the liquid in the driving chamber, a relief valve releasing liquid from the driving chamber to the source chamber when pressure in the pumping chamber exceeds pressure in the driving chamber, means biasing the piston in an unloading direction to reduce pressure in the driving chamber following release of liquid therefrom, and means limiting the unloading stroke of the piston to maintain a volume in the driving chamber filled only by the liquid therein and the air released from said liquid.

21. The diaphragm pump of claim 20 having an inlet valve limiting liquid flow into the pumping chamber on the suction stroke of the diaphragm to maintain a dead space in the pumping chamber accommodating some movement of the diaphragm into the pumping chamber even when saidpumping chamber is closed.

22. The diaphragm pump of claim 20 wherein the means limiting the unloading stroke of the piston maintains a pressure in the driving chamber substantially above the vapor pressure of the liquid therein so that any air released from said liquid follows the law of Henry.

23. A method of pumping fluids under variable flow conditions without varying or stopping the driving input which comprises driving a fluid pumping member with a driving fluid composed of liquid and gas, alternately pressure loading and unloading said driving fluid, releasing some of the driving fluid to provide a reduced driving volume for reduced actuation of said pumping member, and maintaining the pressure on the reduced volume of driving liquid above the vapor pressure thereof to accommodate any expansion of the reduced volume by separation of gas from the liquid.

24. The method of pumping a liquid through full flow, throttled and intermittently stopped conditions without throttling or stopping the driving input which comprises driving a liquid propelling member with a driving fluid composed of liquid and gas, releasing some of the driving fluid to accommodate throttling and intermittent stopping of the pumping, and maintaining minimum pressure on the driving fluid above the vapor pressure of the liquid.

25. The method of pumping through a wide range of flow rates and intermittent stopping of flow without changing driving input which comprises thrusting a driving liquid against a pumping diaphragm, unloading said liquid whenever pumping pressures exceed a predetermined level, and maintaining the liquid at all times above its vapor pressure.

26. The method of diaphragm pumping throughout a wide flow range without changing the driving input which comprises driving a diaphragm with a liquid conof the diaphragm into the chamber even when the chamber is sealed, loading and unloading the driving liquid to reciprocate the diaphragm, releasing driving liquid to accommodate reduced reciprocation of the diaphragm during throttling and intermittent stopping of the pumping, and releasing air from the driving liquid on the suction stroke following the release of excess driving liquid to maintain pressure of the driving liquid always above its boiling point. 

1. A driven fluid pump device adapted to be throttled and stopped without throttling or stopping the driving input which comprises, means defining a pumping chamber and a driven fluid chamber, a fluid propelling member separating said chambers, a driving fluid in said driving fluid chamber actuating said member and composed of liquid and gas, driving means for alternately pressure loading and unloading said driving fluid, means for releasing some of said driving fluid when loaded above a predetermined pressure to provide a reduced driving volume for reduced actuation of said propelling member, and means maintaining minimum pressure on the driving fluid above the vapor pressure of said fluid whereby any expansion of the reduced driving volume upon unloading will be accommodated by the remaining liquid and gas released therefrom.
 2. The device of claim 1 wherein the driving fluid is a liquid having a gas dissolved therein which is released therefrom according to the law of Henry.
 3. The device of claim 2 wherein the liquid is a lubricant and the gas is air.
 4. The device of claim 1 wherein the fluid propelling member is a diaphragm.
 5. The device of claim 1 wherein the driving means is a piston.
 6. The device of claim 5 wherein the piston has a uniform stroke.
 7. The device of claim 5 wherein the piston is driven by an eccentric member.
 8. The pump device of claim 1 wherein the fluid propelling member receives pumpage on one side and said driving fluid on the other side and an inlet valve controls flow of pumpage to maintain a dead space on the pumpage side of said fluid propelling member accommodating movement of the member to lessen reduction of the driving volume of said driving fluid during standby operation when no flow of pumpage occurs.
 9. The device of claim 8 wherein the fluid propelling member is a diaphragm having a pumpage chamber on one side and a driving fluid chamber on the other side, an inlet valve controls flow of pumpage into the pumpage chamber, a check valve controls flow out of the pumpage chamber, and said two valves cooperate to prevent the pumpage chamber from being completely filled to maintain a dead space of compressible fluid accommodating movement of the diaphragm into the pumpage chamber during throttling or stopping of the pumping.
 10. The device of claim 1 including a supply chamber for driving fluid and a spring loaded valve controlling release of driving fluid to said supply chamber.
 11. The device of claim 10 wherein a passageway selectively connects the supply chamber with the driving fluid chamber ahead of the driving means for replenishing said chamber.
 12. A driven pump adapted to be throttled or stopped without throttling or stopping the driving imput comprising a housing defining a pumping chamber and a driving liquid chamber, a fluid propelling member separating said chambers, driving means acting on liquid in the driving liquid chamber to actuate said propelling member for pumping fluid through the pumping chamber, a relief valve controlling maximum pressure in said driving liquid chamber and releasing excess liquid from the chamber to accommodate throttled movement of the diaphragm, and means controlling the driving means to maintain pressure on the remaining liquid in the driving liquid chamber above the vapor pressure of the liquid.
 13. The pump of claim 12 having a source of driving liquid containing gas dissolved therein communicating with said relief valve to receive excess driving liquid from the driving liquid chamber, and means connecting said source with the driving liquid chamber to replenish the chamber whenever pressure therein is below the pressure of the source.
 14. The pump of claim 12 wherein the pumping chamber is fed through an inlet valve biased to closed position to maintain a dead space accommodating movement of the fluid propelling member into the pumping chamber even when the chamber is closed.
 15. The pump of claim 12 wherein the fluid propelling member is a diaphragm and the driving means is a constant stroke piston.
 16. A driven diaphragm pump adapted to be throttled and stopped without throttling or stopping the driving input which comprises a housing having a diaphragm chamber, a diaphragm in said housing spanning said chamber and dividing the chamber into a pumping chamber and an opposed driving liquid chamber, a spring biased inlet valve for admitting pumpage to said pumping chamber, an outlet valve controlling flow of pumpage from said pumping chamber, a source of lubricating liquid having air dissolved therein, means bleeding liquid from said source to said driving chamber, a relief valve controlling flow of liquid from the driving chamber back to the source, a piston acting on liquid in said driving chamber to load and unload said liquid for reciprocating said diaphragm to draw pumpage through the inlet valve into said pumping chamber and to discharge pumpage from the pumping chamber through the outlet valve, means driving said piston through a stroke to act through the liquid for forcing a full stroke of the diaphragm whenever pressure in the pumping chamber is below the pressure of the driving liquid, said relief valve releasing driving liquid from the driving chamber back to the source when pressure in the pumping chamber exceeds pressure on the driving liquid, the spring load on said inlet valve to the pumping chamber being effective to maintain a dead space in the pumping chamber accommodating movement of the diaphragm into the pumping chamber even when the outlet valve is closed thereby minimizing release of driving liquid through the relief valve upon throttled operation of the pump, and means limiting the stroke of the piston to maintain the driving liquid volume less than a volume occupied by the liquid and available air from the liquid to always sustain the liquid above its vapor pressure whereby reduced throttled diaphragm strokes are accommodated by reducing the volume of driving liquid and releasing air from the reduced volume of liquid to prevent vaporization of the liquid.
 17. The pump of claim 16 wherein the piston closes the bleeding means except at the end of its suction stroke.
 18. The pump of claim 16 wherein the piston is spring biased against a wobble plate providing the driving input.
 19. The pump of claim 16 wherein the outlet valve is in a spraygun receiving pumpage from the pumping chamber.
 20. A diaphragm pump comprising a housing defining a chamber for a source of lubricating liquid containing dissolved air, a driving chamber for said liquid and a pumping chamber, a diaphragm separating said driving and pumping chambers, a piston separating said source and driving chambers, means reciprocating said piston to load and unload liquid in said driving chamber, a passageway venting the source chamber to the driving chamber only when the piston unloads the liquid in the driving chamber, a relief valve releasing liquid from the driving chamber to the source chamber when pressure in the pumping chamber exceeds pressure in the driving chamber, means biasing the piston in an unloading direction to reduce pressure in the driving chamber following release of liquid therefrom, and means limiting the unloading stroke of the piston to maintain a volume in the driving chamber filled only by the liquid therein and the air released from said liquid.
 21. The diaphragm pump of claim 20 having an inlet valve limiting liquid flow into the pumping chamber on the suction stroke of the diaphragm to maintain a dead space in the pumping chamber accommodating some movement of the diaphragm into the pumping chamber even when said pumping chamber is closed.
 22. The diaphragm pump of claim 20 wherein the means limiting the unloading stroke of the piston maintains a pressure in the driving chamber substantially above the vapor pressure of the liquid therein so that any air released from said liquid folLows the law of Henry.
 23. A method of pumping fluids under variable flow conditions without varying or stopping the driving input which comprises driving a fluid pumping member with a driving fluid composed of liquid and gas, alternately pressure loading and unloading said driving fluid, releasing some of the driving fluid to provide a reduced driving volume for reduced actuation of said pumping member, and maintaining the pressure on the reduced volume of driving liquid above the vapor pressure thereof to accommodate any expansion of the reduced volume by separation of gas from the liquid.
 24. The method of pumping a liquid through full flow, throttled and intermittently stopped conditions without throttling or stopping the driving input which comprises driving a liquid propelling member with a driving fluid composed of liquid and gas, releasing some of the driving fluid to accommodate throttling and intermittent stopping of the pumping, and maintaining minimum pressure on the driving fluid above the vapor pressure of the liquid.
 25. The method of pumping through a wide range of flow rates and intermittent stopping of flow without changing driving input which comprises thrusting a driving liquid against a pumping diaphragm, unloading said liquid whenever pumping pressures exceed a predetermined level, and maintaining the liquid at all times above its vapor pressure.
 26. The method of diaphragm pumping throughout a wide flow range without changing the driving input which comprises driving a diaphragm with a liquid containing a gas dissolved therein and releasing gas from the liquid under the law of Henry to accommodate throttled and intermittent stoppage of the pumping operation.
 27. The method of diaphragm pumping a liquid throughout a wide range of flow and intermittent stopped conditions without throttling the driving input which comprises driving the diaphragm with a liquid containing a dissolved gas, controlling the flow of liquid into the diaphragm pumping chamber to maintain a dead space in the chamber accommodating movement of the diaphragm into the chamber even when the chamber is sealed, loading and unloading the driving liquid to reciprocate the diaphragm, releasing driving liquid to accommodate reduced reciprocation of the diaphragm during throttling and intermittent stopping of the pumping, and releasing air from the driving liquid on the suction stroke following the release of excess driving liquid to maintain pressure of the driving liquid always above its boiling point. 